Apple released the original iPod six years ago on October 23, 2001. During its first six years, the iPod has gone from a 5GB Mac-only music player to a cross-platform 160GB music and video player and the most popular media player on the market. Happy birthday, iPod.

Apple's original iPod

The first iPod cost US$399 and measured 2.43 x 4.02 x .78-inches. In comparison, the 160GB iPod classic -- the model that most closely physically matches the original -- costs $349, and measures 2.4 x 4.1 x .53-inches. Where the original was essentially just a music player, later models added the ability to play videos and even games.

In January 2004, Apple introduced a smaller form factor model called the iPod mini. The smaller sized unit shipped with a 4GB hard drive and was available in silver, pink, gold, blue, or green. The popular iPod mini was replaced in September 2005 with the iPod nano.

Analysts and Apple fans questioned the company's decision to kill the wildly popular mini and replace it with the flash-based nano. In the end, however, it appears that Apple knew exactly what it was doing because the nano went on to become the best selling iPod model.

While the original iPod nano shucked the metal body found on the mini, later models returned to the more durable shell. Where the plastic-clad nanos were available only in black or white, the metal clad versions, including the recently released third generation model, were available in several colors.

The iPod lineup was rounded out in January 2005 when Apple introduced the gum stick-shaped iPod shuffle during Macworld Expo. It was later replaced with the an even smaller second generation model in September 2006. Both were flash-based, like the iPod nano, but did not include a display. The shuffle's compact size and low price helped it to become surprisingly popular as well.

Apple introduced a special edition iPod nano in October 2006 as part of the (PRODUCT) RED promotion to raise money for AIDS programs in Africa. The special edition models carried over into the third generation iPod nano and iPod shuffle.

In June 2007, Apple turned the iPod on its ear, or at least its side, with the release of the highly anticipated iPhone. The iPhone blended a video capable iPod, Wi-Fi based Web browsing system, and a cell phone into a single unit. It included a multi-touch interface, automatically rotated its display when held upright or pivoted on its side, and became a hit with consumers as soon as it was released.

Despite Apple's exclusive distribution deal with AT&T in the United States, over a million iPhones were sold by the end of September.

The iPhone was followed only a couple of months later by the iPod touch: an iPhone-like iPod that lacked Bluetooth and cell phone features.

Even though Apple's iPod road seems to be paved with gold, there have been a few potholes along the way. The iPod has been plagued with a series of lawsuits over batteries, scratched screens, product pricing, and most recently storage capacity.

The iPod's popularity also helped propel the iTunes Store, originally the iTunes Music Store, into the single largest legitimate music download site. When the iTunes Store first launched, it offered just music, but later added music videos, movies, and TV shows. Where other music download services offered music subscriptions, Apple offered music sales, a feature that ultimately has proven to be far more popular among consumers.

The iPod skyrocketed in only a few short years from being a "why would anyone pay that much for a music player?" product to a market dominating must-have device. Apple has been able to maintain that 70 percent-plus market control for the past few years by continuing to update and innovate, and by maintaining an easy to use and slick looking product lineup.

Happy birthday, iPod.